For completeness, you will also have to complete the serialize and Parse functions (This is only required if you want to save/load your material to a .babylon file).
Please note that serialize function needs to output the complete material name to the serializationObject like here:

serializationObject.customType = "BABYLON.SimplelMaterial";

And you're done for the material! Now it is time to test it.

Update the test page

To test your material, open the /materialsLibrary/index.html page. References are added automatically.

Launch the test server

To Launch the server, you can start from the tools/gulp folder:

gulp webserver

Using the material with Babylon.js file loader

Babylon.js file format supports the use of custom material. You must provide a serialize() and a Parse() functions alongside with a getClassName() function.
To let the loader knows about your material, you will also need to add the following line to the code using your material:

Tools.RegisteredExternalClasses["MyMaterial"] = MyMaterial;

This code will add your class to the list of supported external classes so that the loader will be able to instantiate it when loading a .babylon file with a reference to your material.